Router-id BGP and OSPF

[Mahesh Gohil]

Hello Guys,

I was going through use of router-id in BGP and OSPF

The use of R-id in BGP

> Only in BGP path selection criteria not mor than this.

  ? Even in production if R-id get changed what is the impact. 

The use of R-id in OSPF

> Only in case of virtual link. If R-id get changed virtual link  will no longer be operational.

  ? What will be impact of changing R-id if I am not running any virtual link

apart from this how will both protocol choose R-id. apart from basic stuff like the highest loopback address does it also consider interface enabled with vrf and having highest loopback.

I have tried with below config but everytime the R-ID remain as lo99 and not lo123 (but after removing vrf from interface R-idit get changed)..so here want to know how it picks R-id

interface Loopback99
ip address 50.50.50.1 255.255.255.255
end

interface Loopback123
ip vrf forwarding TEST
ip address 101.101.101.1 255.255.255.255
end

thanks to join me to understand this

Regards

Mahesh

[gfcisco31 · Accepted solution]

Hello Mahesh.

The router ID proccess is always choosed from the highest loopback ip addresss , if you have no loopback address it will choose the highest ip address on any interface.   but... i don´t thing an interface with VRF enabled will participate

in the election proccess, because... imagine if we have 2 interfaces in different VRFs but with the same ip address. How it would work ?  That´s why i think the enabled VRF interface won´t join the R-ID election proccess.

From a design perspective ,the best thing is to set the R-ID manually, in my opinion !

I could not find any DOC that could explain the election of R-ID with VRF enabled interfaces, but that´s my opinion.

cheers

[Mahesh Gohil]

Hi,

Thanks for your efforts to think over this topic and I agree with the logic you explained for not including

vrf interface in selection of R-id election algorithm. But the thing is how this actually take place. If i do sh ip int brief it doesn't include vrf and

it just give me output of no. of loopback address enabled.

May be there are something internally to router which we do not know. And that I want to know

Thanks

Regards

Mahesh